Transversely recorded tape



kn ii ly m Feb- 6, 1962 L. D. BARRY 3,020,356

TRANSVERSELY RECORDED TAPE Original Filed May 27, 1952 4 Sheets-Sheet 1eyo 26 a noun nu ul an D wn wnnrx 1 l I l nnmzz un :L5 3 an nun nuINVENTOR.

Feb. 6, 1962 L. D. BARRY TRANSVERSELY RECORDED TAPE Original Filed May27, 1952 F/ELD 4 Sheets-Sheet 2 5/ REPRODUCED 7D GRID ORCATl-IODEOUTPUT- GEM/ND LEAD IN V EN TOR.

Feb. 6, 1962 D. BARRY 3,020,356

TRANSVERSELY RECORDED TAPE Original Filed May 27, 1952 4 Sheets-Sheet 3I #30 V/DEO AMPL lF/ER W050 INVENTOR.

TOZVMMA/D W United States Patent 3,020,356 TRANVERSELY RECORDED TAPELeonard Dodge Barry, Detroit, Mich, assignor to Ampex Corporation,Redwood City, Calif., a corporation of California Original applicationMay 27, 1952, Ser. No. 292,013. Divided and this application Dec. 27,1960, Ser. No.

3 Qlaims. (Cl. 179-1002) This invention relates to tape recorders and inparticular to a method and means for recording and reproducing signalsfor television pictures, sound, and other information.

Magnetic tape recorders have long been made for recording sound andinformation with accompanying efforts to improve the magnetic medium andthereby lower the tape speed or increase the audio frequency response ata given speed. By, providing a recorder which transversely scans thetape together with special circuits for recording and reproducing over awide frequency range this improved tape recorder is not only suitable toapply the required audio frequencies to the tape at a much lower tapespeed, but it is also designed for recording video signals which have afrequency range of about 0 to 4 me. with a linear velocity of tapecomparable to present sound tapes.

One object of this invention is to provide a tape recorder for videosignals by which these signals can be picked up in a televisionreceiver, recorded, and reproduced from the record as often as desiredto be played back on a television picture tube.

A second object is to provide a system of scanning a tape to enable moreinformation to be recorded on a given length of tape.

A third object is to provide a combination sound and video magnetic taperecorder.

A fourth object is to provide a recording system for video whichminimizes critical adjustment, is simple to operate, is convenientlysized, and has tolerances and design suitable for manufacture.

A fifth object is to provide a television recorder which does notinterfere with the viewing of the television program on the picture tubeof the television set from which the video signal is being recorded.

Other objects have been taken into consideration within the limits ofthis invention resulting in further improvements in the art of taperecording disclosed herein.

The development of this invention required consideration of severalproblems.

In accordance with present standard the frequency required to be passedin a video amplifier is 0-4,000,000 cycles/sec. for a high qualitypicture. A good picture can be produced with 304,600,000 cycles, and themore limited the frequency range the poorer the resolution'of thepicture.

The present magnetic recording media have a good level output from 20 toabout 5000 cycles at 3.75"/sec. The output volume is equalized bycircuits to give a practically flat response in this range. Using afigure of 5000 cycles at 3.75"/sec. present day tape will record 1333cycles/inch. The frequency response is directly proportional to thespeed. To record video on tape or wire to include 4 mc. would take 4mc./1333 =3000" of medium/ sec. t

As a feature of this invention a rotary Wheel or disk is provided havingrecording heads thereon appropriately spaced to scan the tape crosswisefor recording and pickup at a peripheral speed of approximately 3000"/sec. The tape is curved to conform to the contour of the wheel.

Keeping the size suitable for portability the following example is givento show the relations of dimensions and be less.

speeds. Calculations are based on accepted television standardsproviding for interlaced scanning 30 frames/ sec., 525 lines/frame, and0-4 mc. video frequency response.

The frequency response required of each horizontal video line is:

254 cy./line 1333 cy./inch Ame A wider tape per horizontal video linerequires a higher peripheral velocity for scanning but would give abetter frequency response and a higher output if needed. A narrowervideo track would give a lower frequency response and output level, butthe peripheral velocity would Allowance for overlap and other factorsmentioned' later requires a wider tape than the line of signal to bereproduced. I

Selecting 8 as the diameter for the wheel the spacing of the magneticheads around the periphery=0.19l".

The retrace takes (0.16 to 0.18) picture Width of video track.

Then picture width=P.W.-O.l9l0.17 P.W.

The tolerance is i0.01 0.l63=i0.0016. This is within standard practiceand is the tolerance of variation for spacing the heads around thewheel.

The number of heads=8 3.l416/0.19l=132 heads.

Increasing the width of the tape to include eight hori 'zontal videolines, the number of heads is reduced to sixteen with a slight increasein diameter.

To reduce the rpm. to 5000 then requires a different number of heads anda larger diameter for equal clarity under given conditions.

Number of heads=525 30 60/(8X5000)=23.6E24 heads.

Diameter=24 0.191 X 8/31416: l 1.67.

Using ring-type heads with a 0.0005" gap a width of 0.01" should besuficient for the pole tips and approxivideo line was recorded perrecorded line across the tape'width since, the lines if aligned properlywould build up a field of picture as the cathode ray does on the tube.The succeeding fields would not be interlaced on the recording but wouldbe interlaced by the picture tube.

It should be understood that any improvement in the frequency responseof the tape or magnetic-heads over present standards would improvethe-picture reproduced, or reduce the r.p.m. or diameter of thewheel'for a given quality of picture, and improve the sizing and speedof the tape and associated parts.

In the drawings:

FIGURE 1 is a'top plan view of the improved tape recording mechanism,the enclosure and electrical circuits being removed;

FlGURE 2 is a front elevation of the recorder shown in FIGURE 1;

FIGURE 3 is an enlarged side elevation of the operating lever assemblyin FlGURE-S l and 2;

FIGURE 4 is an enlarged section view of the tape guide assembly taken online l4- in FIGURE 1;

FIGURE 5 is an enlarged edge View of the wheel in FIGURES l and 2 partbeing broken away to show the coil connections to commutator segmentsand general construction;

FIGURE 6 is a side view of a portion of the wheel shown in FIGURE 5furtherenlarged and broken away to show details of the magnetic headsand segments;

FIGURE 7 is a plan view of a piece of tape to show the sound and videomagnetic track; portions thereof being labeled. The two fields of thepicture are outlined and labeled thereon to show the sequence in whichthey are recorded;

FEGURE 8 is a block diagram of a television receiver with a recorderconnected thereto;

FTGURES 9 and 19 arecombination block diagrams and electrical.schematics of two variations of the recording circuits;

FIGURE 11 is a schematic and reproducing circuits;

FIGURES 12 through 17 are curves representing the signal at successivepoints in the process of recording and reproducing;

FIGURES l8 and 19 are schematic views of two alternative arrangementsfor scanning the tape.

Referring to the drawings and in particular to FIG- URES l and 2, 2% isa supply reel and 22, is a take-up reel for magnetic tape 24, which asseen from FIGURE block diagram of the -1 is inserted between wheel 26and groove 28 of guide 29. Guide 29 as seen in cross section in FIGURE 4has retaining sides fill and 31 and edge covers 32 and 33 wvhich holdthe tape on both sides of wheel 26 so that the tape will not leave thegroove 23 by friction of wheel 26 when rotating against the tape. Guide29 holds the tape against the periphery of wheel 26, groove 28 beingcurved to the radius of the wheel, and guide 29 exerts a light forceagainst the wheel by spring 36 and pivot bar member 33 which beingpivoted at two points 46 and 41 in line hold the guide 2% against wheel26 substantially parallel: to the axis of the wheel. Guide 2% has anmserted cushioning pad or gap 44 at the line of contact of the Wheel andguide so that when the tape is inserted by pushing guide 29 away fromthe wheel the tape, will have a slight give in contact with the wheelwhich will save the tape from excessive wear and provide close evencontact.

An erasing head 4-5 bears on the tape 24 along groove curved to fitgroovelt and help hold the tape in the V groove and steady it. Thedesign'principles of the heads are similar to any used for sound eraseor recording. A.C. erase is not objectionable because slight variationsin the tapes longitudinal magnetism will not effect transverse scanning.The sound could be put on over the whole video track if desired as longas the tilt of the sound recording head is adjusted to the slant of thetransverse scanning and the proper biasing and limiting of the amplitudeof the signals is used.

Wheel 26 is driven by constant speed motor so through coupling 62, shaft63, spur gear 64 engaging spur gear 66, shaft 68 to which wheel 26 isfixed. Gears 64 and 66 increase the speed to shaft 68. Gear 64 ispreferably a fiber gear as should one of every gear set to reduce noiseand vibration. Guard 6% encloses most of wheel 26. Spring Washer 7i)prevents axial movement of wheel 26.

Tape 24 is driven by motor 69 through. beveled gears 71 and 72, shaft'74, worm 76, worm gear 78 fixed on shaft 8d coupled to shaft 82 by afriction clutch 84, and sprocket tooth drive wheel 86 having teeth whichengage holes 68 in tape 24. The tape is moved by this tape transportfrom left to right during record and playback at a speed having a fixedrelationship to the r.p.m. of the wheel 26. Thereby recordings can bereproduced even with slight variation in motor speed.

The take-up reel is driven by its motor 9% during record and playback.The supply reel is driven at a relatively high speed for rewind by itsmotor 92.. This practice is followed in some quality tape recorders.

Lever 94 provides means for the operator to shift from a neutralposition N to either a position for record and playback F in which leverd4 is shown or a position for rewind R. FIGURE 3 shows the details oflever- 94. This lever is pivoted about bearings 96 and 98 on shaft 166.The lever has four parallel arms extending to bearings Hi2 and 103holding shaft and bearings 105 and res holding shaft 82. Shaft 82 hasthe sprocket drive 86 fixed thereon. The friction clutch 84 heldtogether by spring 198 permits slippage whenever worm gear '78 isengaged with worm '76upon the operator moving lever 94 to position F orwhenever the force to pull the tape exceeds a safe limit. The amount ofslippage decreases until the tape gets up to speed.

When lever 94 is brought to positions N and R lever moves guide 29 awayfrom wheel 26 disengaging the tape from the Wheel Lever ill is actuatedby link 112 to lever 94 and bears on 38 in positions N and R.

Lever 94 also actuates switches, not shown, to control power to thereeling motors 9t and 92. The usual switching and safety features shouldbe provided.

Wheel 26, as seen in FIGURES 5 and 6, is composed of two nonmagneticdisks 116 and 117 bolted together with bolts 318. Disk 117 is brazed orotherwise secured to shaft 68. Recording-reproducing heads 120 aresymmetrically spaced about the circumference of wheel 26 in a space122-provided by grooving the adjoining faces of each disk. Each head hastwo coils 124 and 125'. The two coils are connected series aiding andthe ends brought to individual commutator segments arranged in twoconcentric rings 126 and 12.7 around the side of the disk 116. The coilsare similar and similarly connected to the segments so that any signalrecorded or picked up will have the same polarity and value independentof which head recorded or picked it up. The cores 123 are in two partsto facilitate winding and are securely fastened to disk 116 by screws12? through overlapping parts of the cores 128. Copper brushes 132, and133 engage concentric rings 126 and 127 respectively to carry thesignalsbetween the coils and the recording-reproducing circuits. Thecornmutator segments and brushes I prefer to call electrical switchingmeans.

When in reproducing a head comes in or out of contact with the magneticmedium at the ends of the line being scanned the coils receive a voltagesurge from any magnetization from the signal, bias, or erase that ispresent. This is not part of the signal to be picked up; it is adiscontinuity which has caused this surge. Therefore the signal isrecorded with enough overlap in scanning sue-- cessive lines to providefor the period of this voltage surge teen-d before the coils arecontacted by the brushes connecting them to the reproducing circuits.This is easily done by changing to a' narrower set of brushes than wereused for recording or by using separate coils and a commutator ring forpickup with brushes having the desired coverage. A slip ring couldprovide a commom for one side of all coils. The recording should be madewith sumcient overlap so that there will still be a slight amount ofoverlap with the narrower brushes to prevent an open circuitinterruption of the signal.

FIGURE 7 shows the tape 24 as it would pass under the heads shown inFIGURE 6. The tape has a sound and a video track so labeled. Fields 1and 2 follow in sequence and are composed of a suitable number ofhorizontal lines of video per line of width labeled Reproduced Signal.To pick up this Reproduced Signal the video track includes Alignment andContact Allowance that is an overlap provided for the distance requiredby the brushes to come from no contact to sufficient contact with thesegments and allowance for tolerance in spacing heads, commutatorsegments, positioning of guide 29, and other variables. This overlapadded at the entrance and exit of the Reproduced Signal equals thePicked Up Signal. Adding Voltage Surge Allowance gives the requiredminimum Recorded Video Signal per transverse line. The magnetic mediumcan be wider than this minimum width.

Referring to FIGURES 8, 9, and 10, the recorder picks up a signal at theoutput of the video detector where it has been rectified and filtered ofthe LF. carrier. The recorder is preferably provided with its own videoamplifier with circuits designed to give any desired pre-emphasis as insound recorders to balance the response over the frequency range. Thesignal is put in the video amplifier. The output thereof is connected toa DC. restorer, FIGURE 9, as required if the circuits of the videoamplifier do not pass the DC. component and so that the signal mightalso be picked up after any T.V. video amplifier as indicated by dashlines FIGURE 8. In FI URE 10 the DC. restorer. was. omitted. The signalis next fed to a novel amplifier one form of which is shown in FIGURE 9and another form in FIGURE 10.

Referring to FIGURE 9, the signal is then applied to the grid of tube140. A voltage supply B1+ is connected to the plate of tube 14-0 throughresistors R1 and R2. R1 being connected between 31+ and a junction pointI 1. The circuit of the head coils 124 and 125' is connected by segments126 and 127 respectively engaging brushes 132 and 133 across points J1and 32+ in series with an equalizing network represented by a condenserC1 and resistor R3 in parallel. 132+ has a potential equal to or lessthan B1+. Grid bias is provided for tube 140 across R4. The input signalwould probably vary from 0 to 75 volts. The zero voltage signal on thegrid would represent a white picturein the T.V. cathode ray tube and 50to 75 volts black. Tube 140 is fully conducting with zero grid volts anddecreases in conductivity linearly from 0 to 75 volts. I1 is at aminimum potential for this point when tube 140 is fully conducting andmaximum when tube 140 is nonconducting. The difference in potentialbetween 11 at max. and min. can be adjusted by varying R1, R2, and B2+so that the current through coils 124 and 125 can vary as desired.Adjustment canbe made to give varying D.C., A.C. with a DC. component,or pure A.C. Varying D.C. can thus be provided having the proper DC.bias for recording. Or using an A.C. bias oscillator of high frequencythe adjustment is made to pro vide A.C. alone.

Referring to FIGURE 10, this circuit for driving the coils differs fromthe circuit in FIGURE 9 in that two tubes are used in place of 140 and acomplete bridge circuit is formed. The bridge is formed by tubelStt inseries with resistor R10 and tube 152 in series with resistor R11 inopposite legs of the bridge, the plate side ends of the legs of bothtubes 150 and 152 connected together by a third leg containing resistorR12, and the cathode side ends of the legs connected together as thefourth leg containing resistor R13. The plate side of the leg of tube152 is connected to voltage B3+ and the cathode side of the leg of tube150 is grounded to B3. Coil 124' with equalizing circuit represented byC3 and R14 is connected as a bridge from the plate side of the legcontaining tube 150 to the cathode end of the leg containing tube 152.The tubes are pentodes or triodes and have their grids connected to theinput signal and biased to a negative potential B4- connected to thegrids by a high resistance R15.

When the tubes are full conducting with zero grid voltage, for example,current flow is from B3+ to B3- through tube 152, R11, coil 124, R10,and tube 150 in series. The tubes decrease in conductivity linearly asthe grid voltage swings from 0 to 75 volts and as they do the potentialacross the bridge changes linearly. The polarity and potential acrosscoil 124 is determined'for a given signal input according to the biasingof the grids, tube characteristics, and values selected for theresistors. The plate voltage is high enough to provide linear operation.Thus varying D.C., A.C. with a DC. component, or pure A.C. can beprovided. The proper values being selected according to whether A.C. orDC. biasing is used as with the circuit in FIGURE 9.

Steps in the process of recording and reproducing a signal are shown byreference to FIGURES 12 through 17.

FIGURE 12 shows a typical signal from the T.V. de-

tector, not to scale.

The A.C. bias frequency should be several, times the 7 block diagramwith an adjustable resistor R5 to select the best biasing current. Theoscillator output circuit is tuned by a small capacitance C2 andinductance L to prevent shorting of the signal through the oscillator.

FIGURE 13 shows the output from an odd number of amplifier stages thusreversing the signal, the D.C.'voltage component being restored by theDC. restorer if it was missing at input or lost in the video amplifier.

FIGURE 14 shows the signal as recorded with DC. biasing, the polarity ofthe bias voltage being such as to reduce the magnetization left by thesaturating erase magnet. If a minus voltage was used for biasing thetape the zero reference line would'be'at the top by an-equal distanceabove the bias voltage line. The Max.. and Min. lines represent therecording current at limits of linearit of recording on the magneticmedium.

FIGURE 15 shows the signal with DC. components, removed ready forrecording with A.C. biasing.

FIGURE 16 represents the net signal recorded with either A.C. or DC.biasing. The flux lines are omitted for simplicity. The flux density isindicated by the distance the curve departs from the zero referenceline. The flux lines if shown would loop from the vertical faces only.Lines through the zero reference represent complete reversal of thedirection of magnetization as indicatedby the letters N and S.

FIGURE 17 shows the signal voltage picked up by'the coils. Each increaseof magnetization in one directioninduces a voltage of one polarity, andeach decrease or reversal of magnetization therefrom induces a voltageof the opposite polarity in the coils. The intensity of this inducedvoltage in either case is proportional to the rate of change of fluxlinking with the coils.

The circuit shown in FIGURE 11 is a practi'calmeans developed toreproduce the original signal. This circuit receiving these intermittentvoltages adds and subtracts charges in accordance with the voltageinduced with reference to-a linear rate of charging and dischargingcon-j denser C4. The amplifying portion of this circuit is assumed to bedesigned to supplyv post-emphasis.

Referring to this circuit, two similar tubes and 161 are provided. Oneend of the pickup coil 124 is connected to the grid of tube 160 and theother endconnected to the grid of tube 161. Equally matched resistorsR21. and R22 connected in series across the grids of tubes 161i and 161provide a balanced grid bias voltage from a source of negative potential85-. The cath odes of tubes the and 16?. are grounded, and the platesare connected in series with equal resistances R23 and R24 respectivelyto 36+ voltage supply. The plates of tubes 163 and 161 are alsoconnected to the grids of tubes 164 and 165 respectively in series withcondensers C and C6 respectively. Grid leak bias is provided for tubes16 i and 165 by resistors R25 and R26 respectively. The cathode of tube165 is grounded through R27 and the plate connected to the cathode oftube 164. The plate of tube 364 is connected in series with resistor R23to a positive potential B7}-. The plate of tube 165 is connected tocondenser C4 in series with a current limiting resistor R29 to for-m anintegrating circuit. The other side of C4 is grounded. The output acrossCd is fed to the grid of a video amplifier providing if desired furtherpost-emphasis from which the signal is returned to the TH. ahead of itsvideo amplifier as seen in i lGURE 8. The circuit connecting therecorders output to the T.V. has a high resistance R36 in series toprevent excessive current caused by improper connection or operation.The connecting leads should be fused where the recorder is to be aseparate unit connected and disconnected from the T.V. set.

A voltage induced in coil 12% will place opposite charges on the gridsof tubes 16% and 16-1. The bias voltage supplied by B5. will be suchthat the tubes 16d and .161 will operate as class A amplifiers. When nosignal is being received condensers C5 and C6 have equal charges and thebiasing can be such that tubes lot and 161 conduct. A signal will causeone tube to conduct more and the other less according to the polarity ofthe signal. The tube which conducts less increases the charge on itsplate condensers and this increases the positive value of the grid ofthe associated tube 164 or 165 causing this tube to conduct if biased tocutoff with no signal or to conduct to a greater extent if not biased tothat extent.

With a sufiiciently high voltage applied at 137+, tube 164 conducts,charging the upper plate of capacitor C4 positive and the plate of tube155 positive until tube 1655 becomes conductive. A positive signal(reduction of negative charge) on the grid of tube 165 will causeconduction, reducing the, positive charge on the upper plate of Cdandthe cathode of tube 164 enabling tube 164 to be more readily conductivewhen its grid receives. a positive charge, thus-capacitor C4 gains andloses charges above and below its initial charge. The signal. isalgebraically integrated: on condenser C4 in'that both positive andnegative charges are added thereon, the negative being subtracted fromthe positive.

Tubes 164' and 165 will be biased to the same. point of conductivitywith no signal and are preferably biased to cutoff With no. signal. Thuswhen a signal increases the grid potential of tube 164 that tubeconducts and increases the potential. on C4. When a signal of reversepolarity is received this increases the grid potential of tube 153,- andthat tube conducts and decreases thev potential on C4. Thus the chargeon C4 can be added and subtracted. The circuitis balanced to add andsubtract charges on condenser 04. on a linear basis, whereby the outputvoltage across 04- is proportional to fEdt of the applied signal voltagewhich will be pure A.C. as seen from FIGURE 17' and therefore balanceout the signal charge on C4. The effect of a signal charge on C4 in influencing conductivity can be made negligible. The cathode oftube 165can beconnected to. a negative potential below ground if this is founddesirable to enable it to have a sufficient potential difference betweenplate and When reproducing a recorded signal on a TV. receiver the linesof recording are synchronized with the scanning of the tape by retardingthe tape manually by applying a slight force to slipping clutch 84,FIGURES l, 2, and 3, until the wheel 26 scans on the lines and notbetween lines it the recording was made with space between lines;otherwise this adjustment is not necessary. The magnetic head scanningwheel 26 should be free from wobble and vibration, and is held againstaxial movement as described so that the path of the magnetic headstherein will not vary beyond allowable tolerances.

Two variations in the arrangement for scanning are shown in FlGURES 18and 19. Other methods of scanning tape with transverse movement includea reciprocating head or heads, and heads mounted on and moved by endlessbelt.

FTGURE 18 shows two tapes 24 and 24 being scanned by wheel 26' the headsthereof being located on the side in a ring contacting the tapes andconcentric with the axis of the wheel. The resulting transverse scanwill be curved to the radius of the circle of the heads and will enablea slightly longer transverse line for a given width of tape than withthe scanning wheel rotating perpendicular to the face and edge of thetape. The tape is flat when scanned. Rollers and 181 hold the tapes 24and 24 respectively against the heads on wheel 26. Two or more tapes canbe simultaneously scanned by one wheel and two or more recording andreproducing circuits provided. Some applications are the making ofseveral recordings, theblending of pictures, or the quick change fromone tape recording. to another.

FIGURE 19 shows disk 26" scanningtape 24 at an angle. This inclinedscanning is intermediate between the type of scanning shown in FIGURES 1and 2 and that shown in FIGURE 18. The curvature of the tape is reduced'as the angle of the wheel from perpendicular is increased.

Variations inthe type of magnetic heads, the circuits for recording andreproducing, the contacts between the Wheel and the stationary circuitsand other variations may readily come to mind herewith. This recordercan be adapted to record sound or information at very slow tape andscanning wheel speed simply by providing a slow speed drive; forexample, motor 60 could be replaced with a gear motor. This recorder canbe developed for use in conjunction with a T.V..camera for recordingpictures for later broadcast orv for direct replay onindividual T .V.receivers. 1

Magnetic tape is also called magnetic film especially when used in i6and 35 mm. sizes. The wordmagnetic tape is herein meant to includemagnetic film.

This application is a division of my prior application, Serial No.292,013, filed May 27, 1952 and now abandoned.

Although I have shown and described only one form of recorder, togetherwith a few variations of the method of scanning, embodying my invention,it is understood that various changes, modifications, and adaptationsmay be made therein Wtihin' the scope of the appended claims withoutdeparting from the spirit and scope of my invention. I

What is claimed is:

l. A recording film, a signal recorded on said film in a line runningtransversely of said film, which line is continued longitudinally ofsaid film by another line running transversely of said film, a portionof the. end of the first said line and the beginning of its continuationline being simultaneously recorded at substantially the same recordingstrength as that in the central portion of the recorded lines, therebyproviding an overlap.

2. A recording film, a signal recorded on said film in lines runningtransversely of said film, said signal being continued in lineslongitudinally displaced from each other along the film, the signalrecorded being overlapped at the ends and beginnings of the lines at thesame recording strength as that in the central portion of the recordedlines.

3. A recording tape, a first signal recorded on said tape in a firstline running transversely of said tape, which line is continuedlongitudinaly of said tape by a second line running transversely of saidtape, a portion of the end of said first line and the beginning of saidsecond line being simultaneously recorded at substantially the samerecording strength as that in the central portion of the recorded lines,thereby providing an overlap, and a second signal recorded on said tapein a line runing longitudinally of said tape adjacent one edge thereof.

References Cited in the file of this patent UNITED STATES PATENTSMarzocchi June 10, Schuller June 20, Carmel Sept. 24, Roth Mar. 2,Masterson Dec. 4, Coutant et al. Nov. 19, Fries June 17, Carnras Aug.18,

